Fine and ultrafine particulate organic carbon in the Los Angeles basin: Trends in sources and composition

Abstract

In this study, PM2.5 and PM0.18 (particles with dp < 2.5μm and dp < 0.18μm, respectively) were collected during 2012-2013 in Central Los Angeles (LA) and 2013-2014 in Anaheim. Samples were chemically analyzed for carbonaceous species (elemental and organic carbon) and individual organic compounds. Concentrations of organic compounds were reported and compared with many previous studies in Central LA to quantify the impact of emissions control measurements that have been implemented for vehicular emissions over the past decades in this area. Moreover, a novel hybrid approach of molecular marker-based chemical mass balance (MM-CMB) analysis was conducted, in which a combination of source profiles that were previously obtained from a Positive Matrix Factorization (PMF) model in Central LA, were combined with some traditional source profiles. The model estimated the relative contributions from mobile sources (including gasoline, diesel, and smoking vehicles), wood smoke, primary biogenic sources (including emissions from vegetative detritus, food cooking, and re-suspended soil dust), and anthropogenic secondary organic carbon (SOC). Mobile sources contributed to 0.65±0.25 μg/m3 and 0.32±0.25 μg/m3 of PM2.5 OC in Central LA and Anaheim, respectively. Primary biogenic and anthropogenic SOC sources were major contributors to OC concentrations in both size fractions and sites. Un-apportioned OC (“other OC”) accounted for an average 8.0 and 26 % of PM2.5 OC concentration in Central LA and Anaheim, respectively. A comparison with previous studies in Central LA revealed considerable reduction of EC and OC, along with tracers of mobile sources (e.g. PAHs, hopanes and steranes) as a result of implemented regulations on vehicular emissions. Given the significant reduction of the impacts of mobile sources in the past decade in the LA Basin, the impact of SOC and primary biogenic emissions have a larger relative impact and the new hybrid model allows the impact of these sources to be better quantified.

Associations of oxidative stress and inflammatory biomarkers with chemically-characterized air pollutant exposures in an elderly cohort

“…Furthermore, with considerably greater resources than the present study, the previous study measured air pollutants at the residential location (retirement communities) of each subject group that likely greatly reduced exposure error. Another possible explanation for why our current results for the systemic biomarkers are not as definitive as our previous studies could be due to the fact that the air pollutant levels, especially ultrafine PM, EC, OC, and tracers of mobile sources measured by our research group, have decreased over the last decade in the Los Angeles area (Shirmohammadi et al 2016). This resulted from more stringent regulations on mobile source emissions by the United States EPA, California Air Resources Board and SCAQMD (Hasheminassab et al 2014a).…”

The relative importance of tailpipe and non-tailpipe emissions on the oxidative potential of ambient particles in Los Angeles, CA

“…The contribution of secondary ions to PM 2.5 mass concentration was 33 and 31% in Central LA and Anaheim, respectively, while in the PM 0.18 size fraction they accounted for 13 and 14% in Central LA and Anaheim, respectively. More details on aerosol chemical composition and mass concentrations are discussed elsewhere 31 .…”

“…The results discussed in the previous section revealed that vehicular abrasion, an important component of non-tailpipe emissions, together with secondary OC, were two major sources significantly contributing to PM 2.5 DTT activity, in addition to tailpipe emissions. Shirmohammadi et al 31 recently showed that important tracers of tailpipe emissions in PM 2.5 and PM 0.18 such as PAHs, hopanes and steranes concentrations have decreased by 40–70% and 50–70%, respectively over the past decade in Central LA. These findings, along with the comparison of ultrafine PM redox activity with previous studies, corroborate the effectiveness of stringent regulations on vehicular tailpipe emissions in reducing the overall ambient ultrafine PM toxicity.…”

“…The model estimated the relative contributions from mobile sources (including gasoline, diesel, and smoking vehicles), wood smoke, primary biogenic sources (including emissions from vegetative detritus, food cooking, and re-suspended soil dust 43 ), and anthropogenic secondary OC (SOC). The details of the CMB analysis can be found in the above companion paper 31 . OC source apportionment results from the CMB model were converted to PM 2.5 and PM 0.18 mass concentrations to evaluate the source contributions to total mass, using the OC-to-PM ratios for the wood smoke and mobile source profiles 44,45 .…”

Source Apportionment of Inorganic and Organic PM in the Ambient Air around a Cement Plant: Assessment of Complementary Tools

“…As it has been found in other studies our results indicate that main sources of the finest PM components are linked with combustion processes. In fact, major sources of fine particles in urban areas are vehicular emissions especially of diesel vehicles (Shirmohammadi et al, 2016). In our case, however biomass combustion also seems to have a considerable contribution in PM 2.5 and PM 1 levels what could be related to the plant activity.…”